It first depicted on the cover of the original first edition Manual of the Planes (Jeff Grubb, 1987). Although the book contained no statistics for the creature, it did make mention of the creature as an "ethereal dreadnought".[1]

First described in second edition for the Planescape setting in the Planescape Monstrous Compendium II (TSR, 1994), by Rich Baker.[2]

They attack characters wandering around the Astral Plane by attacking their silver cords (the link between a character's physical body and their astral form, which, if severed, will kill the character instantly). They also make use of powerful anti-magic to weaken characters who are dependent on magic items and spells as sources of power.

Astral dreadnoughts are solitary creatures, with no form of society, and seem to lack any form of motivation other than to devour any astral travellers who are unfortunate enough to cross its path. Very few have ever encountered an astral dreadnought; nobody has ever managed to communicate with such a creature and lived to tell the tale.

The astral dreadnought is a gargantuan creature, reaching approximately the same size as a storm giant. It has a single, black eye in the middle of its face (similar to that of a cyclops), and a gaping maw filled with razor-sharp teeth. Its tongue is dark blue. Its armored carapace is a reddish-brown colour, covered with a multitude of horn-like spikes. It has two muscular forearms, which end in huge pincer-like claws. Its lower body is serpentine.

Some speculate that the astral dreadnought may not be a native of the Astral Plane, because its tail appears to have no end; rather, the infinitely long, silver cord which trails off from the creature's 'tail' would imply that the astral dreadnought is, in fact, projecting its spirit from some unknown, material world.

The astral dreadnought attacks using its claws and teeth in melee combat. It may try to devour its opponent by grabbing them with its claws and stuffing them into its gaping mouth, swallowing them whole. Whilst a swallowed opponent may cut its way out of the creature's belly (despite suffering large amounts of crushing and acid damage), the Astral Dreadnought may chew through and sever their opponent's silver cord.

The astral dreadnought’s eye continually produces an anti-magic cone, with extends in front of the creature at a range of up to 60 feet.

It also uses fear gaze to terrify its opponents, with a range of 60 feet (with effects equivalent to those of a fear spell cast by a 20th level sorcerer).

All magical and supernatural powers and effects within the creature's anti-magic cone are suppressed — including the astral dreadnought's own fear gaze. Therefore, the astral dreadnought must choose whether to activate or deactivate its anti-magic cone in order to allow the use of fear gaze.

The astral dreadnought is often cited as one of the inspirations for the design of the original Cacodemon enemies from the Doom series of first-person shooter video games. In fact, the artwork used for the original Cacodemon sprites is widely considered to be a replication of an illustration of an astral dreadnought from the Dungeons & DragonsManual of the Planes1.